1. Field of the Invention
This invention relates generally to control apparatus and more particularly to clutch controlling apparatus which is used upon motor vehicles, especially industrial vehicles.
2. Description of the Prior Art
In general, industrial vehicles such as for example, a forklift vehicle equipped with an automatic transmission having a torque converter are often operated under full-load conditions of the engine in order to perform cargo-lifting operations, and furthermore, such operations often require forward and backward inching-type movements of the vehicle. In order to easily attain such movements, it is conventional to equip the vehicle's transmission with an inching valve which is actuated correspondingly with the brake pedal of the vehicle so as to maintain the clutch of the transmission in a semi-clutched condition.
In most of such conventional structures, the inching valve control for maintaining the clutch of the transmission in the semi-clutched condition is actuated upon an idle stroke of the brake pedal while the brake of the vehicle is actuated by the remaining stroke of the pedal. Hence, problems are not usually encountered when employing the vehicle upon level land, although it is sometimes quite dangerous to employ the vehicle upon land which slopes downwardly. For example, when performing a lifting operation upon land which has a downward slope, if the brake of the vehicle is actuated and inactuated so as to provide inching movement of the vehicle when lifting the vehicle's transmission has its clutch repeatedly actuated and inactuated so that at particular instances the vehicle is permitted to move under the influence of gravity an undetermined distance in an uncontrolled fashion whereby it may possibly collide with some obstacle or person.
In order to obviate these problems, it has been proposed to employ structure which includes two brake pedals, one of which actuates the brake of the vehicle and the other of which actuates both the brake of the vehicle and the inching valve by an interlocking mechanism. It has also been proposed to employ structure having a brake-holder for maintaining the brake fluid pressure within the brake fluid system when the brake pedal is depressed. However, the former structure requires two types of brake systems, such as for example, a brake pedal or a brake master cylinder, so that a driver is obliged to selectively depress the brake pedals depending upon the conditions present, such action of course being quite troublesome. Similarly, the latter structure requires means whereby fluid pressure to the piston-cups of the brake system is always maintained so that the possibility of having an accident is increased, and furthermore, the system will be more costly because of the additional brake-holder assembly.